Nanoparticles have sparked interest and excitement among the research community in the last decade. Gold nanoparticles, in particular, have potential applications in various fields like catalysis, biomedical engineering, energy conversion, electronics, photonics, sensors etc. To harness the novel properties of gold nanoparticles it is essential to have a synthesis route that has control over size, shape and polydispersity.
Many routes for producing nanoparticles are solution-based redox reactions, commonly referred to as wet synthesis. Widely used methods for aqueous phase synthesis of gold nanoparticle involve the reduction of chloroauric acid with i) trisodium citrate, or ii) a mixture of tannic acid and trisodium citrate that forms nanoparticles with mean size ranging from 3.5 nm to 16 nm depending on the amount of tannic acid with respect to citrate. It has been reported that lower pH of reducing agent results in bigger nanoparticles. Protocols are performed at elevated temperature, viz. 100° C. and 60° C. respectively.
Other protocols for synthesizing nanoparticles at room temperature fail to produce particles over a wide size range with less polydispersity. For example, gold nanoparticles have been prepared at room temperature using hydrazine or sodium borohydride, ascorbic acid, starch, gallic acid and chitosan. In aqueous phase synthesis, gold nanoparticles of size smaller than 3 nm are synthesized using hazardous, strong reducing agents like sodium borohydride and hydrazine. Many attempts have been made to synthesize gold nanoparticles through “green synthesis” approach using starch or glucose, chitosan and soybean, but they do not yield a wide size range of nanoparticles with low polydispersity.